Metamaterials showing chiral features in the optical spectral range have been fabricated with the aim to obtain polarized reflection with high ellipticity.

 

A series of tailored anisotropic and transparent structures of helical Al1-xInxN nanorods were grown using UHV magnetron sputtering on sapphire substrates. Due to an internal in-plane composition gradient across the crystalline structure, the nanorods will tilt relative to the substrate normal. By rotating the substrate step-by-step around its normal during deposition ‘staircase’ helical structures are obtained. The layer thickness for each step is controlled to tailor the nanorods. Samples with different pitch and layer thickness and with right-handed as well as left-handed chirality were grown.

 

Ellipsometric measurements were performed using a dual rotating compensator ellipsometer providing the full Mueller matrix in the spectral range 245-1700 nm at multiple angles of incidence and 0-360º sample orientation. The relation between the optical characteristics of the samples, specifically the ellipticity, and structural parameters such as number of layers, layer thickness and nanorod pitch of the samples, was studied. For certain wavelengths, near circular polarization is observed both for right- as well as left-handed helical structures.

 

Based on the Mueller matrix data, descriptions of the polarization states and degree of polarization in reflection for different incoming states of polarization will be presented.